<style>
    .dom3_list>li:nth-child(2){
        border-bottom: 1px solid red;
    }
</style>
<ul class="dom3_a">
    <li>
        <img src="img/sz_06.png" alt="">
        <div>
            <p>瓷器水杯</p>
            <p><span>2</span>个</p>
        </div>
        <i class="iconfont icon-return"></i>
    </li>
    <li>
        <img src="img/sz_03.png" alt="">
        <div>
            <p>木</p>
            <p><span>2</span>个</p>
        </div>
        <i class="iconfont icon-return"></i>
    </li>
</ul>